I did some research into RV/camper costs, being interested ourselves. I looked mainly at a 2-person camper-van (van conversion) with insufficient space to bring along our 3 sixty-plus pound dogs. I assumed a 21-day rental (19-day trip) even though it's really too short for a great trip, IMO it's the bare minimum time to see a few sights between hither and thither. I've generalized and rounded some numbers to come up with a ballpark idea. It could cost more or less depending on details, specials, season or if over a long weekend. I'm almost afraid to add up the amounts down the left shown in boldface (amounts in regular font that happen to be at the left margin are just part of the description, not an amount to add on) but that'll give a good guide to the price of 3-weeks Vancouver to Toronto through Canada:

Basic Rental
$1,100 for 7 days camper rental, which would cover a Vancouver-Toronto by driving 8+ hours every day for 6 days, this allowing a barely any time at each end to pick up, pack up, empty, gas-up and return the thing. But that won't allow time to figure out how you want to pack your stuff into it, and then do so--that's usually at least another day.
$2,200 rental for another 2 weeks worth of sight-seeing and stopping just because it's nice.

Insurance Upgrade
$672 ($32 per day) insurance upgrade takes the collision deductible from $5,000 to nil and the comprehensive deductible from $500 to $300. Or $525 ($25 per day) drops the collision deductible to $500 from $5,000.

Mileage Charge
$1,260 in mileage for the basic A-to-B trip; using 4,407 km from MapQuest's shortest drive time for an all-Canadian route. This cost is based on pre-purchased blocks of 500 km @ $140 each ($.28/km). The same km paid at the end would be $180, or $.36/km.
$280 in mileage assuming another 1,000 km worth of driving off the basic A-to-B route for sightseeing, groceries, getting to & from campgrounds and whatnot.

One-way Fee
$520 at one website for the "one-way fee", generally non-refundable upon cancellation (to drop off the camper at a different city than where rented). Some web sites aren't very clear about this charge, but you can be certain there will be one. At one site the fee was the same no matter the model of camper. I don't know yet what's industry standard.

Fuel
I come up with approximately
$1,500 like this: I'll be optimistic and hope that being featherfooted and choosing the smallest available unit, one might get close to 15 mpg IMP (25% bigger than US, so 12 mpg US). So I've used 5 km per litre (14.12 mpg IMP or 11.76 mpg US) to figure the A-to-B driving and 3.6 km/l (10.17 mpg IMP or 8.47 mpg US) for sight-seeing, groceries and whatever side trips. But y'know after all that, I'd probably add 20% to my budget because I just don't believe the mileage will be quite that good.

Small Stuff You'll Need or Want
$200-300 worth of flat-rate fees for stuff like toaster, coffemaker, dishes, pots, lawn chairs, folding table for outdoors, etc. While we would use our own, those coming from overseas would be stuck renting whatever you can't do without, or compare to the cost of getting what you can from Goodwill, or borrow from local friends and ship it back to them, or to use paper dishes where there is municipal composting...devil in the details here.

I didn't notice listings to rent a cooler, which you'd want to do because the fridge in a van conversion is usually very small. Depends how much cooking you plan to do. Keep in mind that counter space = zero in this kind of camper. The counter is used up by the wee sink and 2 burner stove so you have to use the table and get a sore back from leaning at a bad angle.
$50 or less to buy one. Plan to buy ice every 1.5-2 days in spring and fall, at least daily in the summer.

Biting-bug-barrier
I also didn't see any listing for dining tent rental at the RV sites I visited, but unless you're going in fall-winter or NEVER sitting outdoors, you need one. Period. Canada is blackfly and/or mosquito country May-September:
$150-200 to buy an easy-up screened tent. There are cheaper ones. JennieG, you don't need this at the time of year you're expecting to travel.

Campground Fees
$665 to $855 assuming $35-45 per night. Some private ones fall in this price range, some will be more. Provincial and National Parks systems are great, may as well use them. Facilities generally aren't rustic as when I was a kid, although some locations may be--full details online. You may be fine, being off season, but may have to hunt for spots at the most popular campgrounds, which can fill up almost a year in advance. Many hold back a percentage for drive-ins, so arrive very early if you are counting on that.

Plus provincial sales tax & GST, of course, except not GST on insurance if I'm not mistaken.

Extra, of course, are your food & drink, souvenirs, propane refills, firewood, tickets to sights and events etc.

Another expense for us in particular
$2,470 ($130/day x 19 days, this one includes tax) to board our 3 full-sized dogs at the open-concept kennel. They always come home happy and tired with no new fears or issues. They are used to a 1-2 hour off-leash walk most days in addition to on-leash time so we deeply hesitate to put them in a $25 per day per dog cage-kennel that gives them 30 mins exercise in a narrow, concrete run full of yuck. Those kennels often come with staff who hold a matching attitude and skill level, so it's not worth the risk of having to un-do behavioural damage. In reality, we'd likely opt for a larger camper (increase by 30-50% the rental cost; double the fuel cost) and move the $130/day boarding budget to the rental line--and take the "whole family."

Anyway that's my first look at the whole idea. Now I know that RV touring is a lifestyle choice not an economy option. And we'll be saving for a while, or else using car+motel for such a trip. Fortunately the dogs are glad to sleep in their crates.