Coming into Canada, the fine people at Canadian border will ask you why you want to come to Canada ?.. etc etc .. Just tell them you are going shopping.
If you are buying gear at a retail store, show them your ID when you make a purchase or at least tell them you are a US citizen , so they can tax exempt you.
I ship electronics to the USA everyday on a retail basis and no taxes charged for shipped items out of Canada to my US customers, but I am not sure about US citizens buying stuff here in person and talking it back in a vehicle to the US ..
ask anyways for tax exempt if you are buying at a store..
If you are buying private or at a retail store, better off to change your money to CAD before coming over, or at least change it at a money exchange before going shopping..
Retail stores may or may not take USD, but if they do, you may not get the exchange rate of the day.
Going back to the US , you won't have to even stop or deal with the customs people here in Canada, but you will have to stop for US customs, and your probably better off telling them what you bought up here and claim it up front ..
If you buy private gear here, get the seller to make you a sales receipt, ask nice and get one made for a bit less than what you actually paid.
( may save you tax $$ going home )
As long as it the receipt seems close to reasonable, you will have no issues at the border going home.
They may charge you a state sales tax, but other than that, I think thats all you be asked to pay going home ..
Have fun ..
