I have a publishing company that I formed for just that reason. I am in the state of Washington, and I registered my business name with the state. Now no one else (in the state of WA) can use that name. The fee is nominal, but I think it is worth it.

Yes, hesperis, DBA means "Doing Business As". If I have a business like a restaurant and called it Margo's Cafe, I would not need to register that name because it's mine. But if I wanted to call it Planet Food (or some such rediculous name) I'd have to register the name. (It would be officially Margo doing business as Planet Food) I think it is pretty much the same in all of the US but it can certainly vary from state to state.

In Canada, I have no clue, but I would suggest contacting the agency that registers business names and I'll bet they'll help,

Margo