banker here. someone said earlier that their bank manager told them the rate is always better in the am. i say, run and find a new bank manager! if you think about it, that would be logisticlly imposible. the us rate picks up where it left off the day before and them moves up or down, depending on what the economy is doing. if it was always lowest in the morning it would have to keep going up and up, never being able to come down again. hope i said that clear. sounds ok to me, but i'm in my own mind.
the main reason there is a difference between bank of canada exchange rates and bank rates is that when the banks purchase money from the bank of canada they charge a premium. they have to have it shipped in and then we have to have it shipped to us so you pay security for this twice.
i say, get yourself a us mastercard (or visa if they have one) and do not pay the 2.5% difference that is charged when you use your canadian card. get yourself a NO FEE us acct. bmo offers both a chequing and savings us acct that has no fees as long as you have a package plan on your main acct and 95% of the banking population has a pacakage plan on their accts. paying a dollar to get my money out would just piss me off. if your bank doesn't offer you a no fee option, switch banks. money is better in your pocket then a banks!
anyway, just be smart with the money. its yours and whether that means saving the dollar shopping across boarder or swithching banks to save it, do it.