As much as you can afford but remember to have enough to be able to pay any duty your government may charge on your purchases. Also make sure you know what and how much you can bring back duty free, etc. If you are in the US for just a day you ll be taxed on just about everything.Either that, or pull the tags off everything and say you brought it with you if asked.
If I m not mistaking the US and Canadian dollar are at the same rate right now, so I would recommend save about $2000 to $3000.Good luck
I would recommend at most 2k. But u could bring less.