I normally will stop at the first bank ATM machine and take out $400, after crossing the border, both directions. This is based upon past experiences. We use it for provincial parks being run on the honor system, or the hosted ones by private concessionaires as more and more BC ones seem to be. Much like more and more are doing in the US. Having cash is also good to have if you get to a more remote road house and find their credit card data line is down. Then it is cash only if you want fuel.
A few times at the honor system collection "pipes", I had been short of cash and put a personal check in for payment. May take a few months after I get home before the check clears but all of them have eventually. I consider the exchange rate, the foreign transaction fee the PP will have in depositing my check and make it for an amount to cover the extra costs they will incur. If the PP charge is $14cnd a night, I will usually make my check out for $16usd to cover the charge, depending on the current exchange rate. I would rather be a bit over than under as the provincial parks of Canada are just as good as they get, anywhere.
Never heard of any problems with extra gas cans or auxiliary tanks. Though I have never carried any, don't expect you would have any problems going through customs. They may take a look and a sniff of them at the border, as fake gas cans are a method of smuggling illegal goods into a country by some.
