the solution: I created a custom envelope in the Stamps.com software (not the web version). My envelope is 4.25x9.5. The Stamps.com #10 is 4-1/8 x 9-1/2. I suppose 1/4" could make a difference, but it seems strange that it didn't effect my last printer.
I only remembered to do this after recalling that I had to create custom postcards for stamps.com because the one supplied by stamps.com wasn't working. So, there you go. Sorry, canon, it was stamps.com all along that was the villain.
