I tend to stop at the first bank after crossing over into Canada and take out $400 at their ATM. It will last me till the return trip, where I will do the same. Some of the cash usages we have are at an ice cream shop, a bar, quick foods, some of the campgrounds use a "drop the funds in the Pipe" method, occasionally I will run across someone selling hand made items I wish to buy, etc. Any remaining Canadian funds, I will use the last day or so of the return trip, to buy fuel. Last summer I had about $40cnd left over which I will take back next time.
You can run into situation where a more remote gas station, may have a credit card machine not working and they only will accept cash. Doesn't happen too often but I have had it occur to us. Not too difficult to put $150 to $180cnd of diesel in my tank.
We have two of the zippered bank money pouches. One we keep US dollars in and the other has Canadian dollars. Canadian businesses are much better about taking US dollars than US businesses are about taking Canadian dollars. the discount rate won't be in your favor normally.
Formerly of Colorado and Alaska
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Alaska Trip 2011 posted
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On our international travel, we've always just stopped at any convenient ATM and made a withdrawal in the coin of the realm, whatever that was. Thus no need to drag around large sums (and risk getting hit over the head). Put it on your debit card, put it on your credit card as a cash advance, either way works just fine, although the latter is probably safer.