Yes, Stilly, a quarter of a litre is quite close to eight fluid ounces or half a US Standard pint. On this side of the border, one pint is (still) twenty fluid ounces Imperial.

250-ml Mason jars (the jam size) usually get scarce in late summer, but they vanished earlier this year than usual, even from Wal-Mart. I doubt that people are canning more than in previous years; Canadian Tire and Wal-Mart have great stacks of the 500-ml and litre jars that are popular for putting up fruit, veg, pickles, tomato sauce and juice. I think it more likely that the manufacturers are making something else — ventilators, I hope.