I'm definitely being overly cautious, but US border patrol is well within their rights and abilities to pull CC statements, which aren't stored within Canada. Who's to say they won't have a flag in their system 1 or 2 years down the line for OCS and individual stores? Then you're put in a position at the border where you admit the truth, and get banned for that admitted use, or lie when the transaction gets flagged during secondary inspection, and get banned for the lie.

Given that I have to cross every day to pay my mortgage and support my family, I just don't care enough about weed to take that small risk.

Also - you can get a prepaid visa if it matters that much.

Weed doesn't matter enough to me to do that.