Things have changed with the central banking system over the years as the electronic system is vastly improved and practically linked to every place of business throughout North America...so in many ways of transactions used today with a debit or credit card, those that use them know how convienient they are as I too use my one and only debit card for mainly fuel purchases (only within the US though).
Since my first time crossing into Canada in 1985 (23 crossings total to date), I always made the habit of converting my US dollars into Canadian dollars in order to minimize the higher exchange rates you were potentially subjected to if you didn't have Canadian dollars onhand, I have yet to ever use a bankcard while in Canada.
The rule of thumb at least thru the early 1990's that I can vouch to was :
Whenever a foreign visitor entered Canada, particularly driving to Alaska you would have to carry sufficient funds (cash on hand) and physically show the customs or immigration officer when requested, (as many remote businesses back then the farther north you were they would not accept bankcards in the past but US dollars in many places were widely accepted as it is still that way today).
Depending where you were if you didn't have Canadian funds onhand, you might be at a place of business that will not accept US Dollars or accept credit or debit cards, or their electronic system might be down in which you would be temporarily stuck by resorting to pay by other means, which ends up being you paying thru other transaction channels you never originally planned for which would be subjected to some form of transaction fee, or conversion fee which are well hidden at times, or resorting to using the US dollar that some business will accept as you will be charged a higher exchange fee, which will easily wipe out any 2% of savings you thought you were going to do.
Bottom line is :
Cash is King - any rare electronic glitch to where a typical bankcard is used will not work whether the system is temporarily down or the database might decide the card is invalid for whatever reason, it is always good to have cash onhand for this reason and be on your way.
Legal tender is the Canadian Dollar in Canada - once you obtain that currency there is no more exchange rate or fee to be subjected to - the Canadian Dollar in Canada will always be worth a dollar within the country.
Being on the Alaska side of crossing into the Yukon with few banks and large businesses in between is more different than say crossing along a more populated southern border area of Canada and the US with a lot more infrastructure of resources to where you might get a better exchange rate for spending a US dollar at a business, however you are still subjected to a higher rate compared what a bank would typically charge to convert.
I too am with the OP on saving a few bucks if possible by not having to pay for some one elses retirement with fees or other form of currency transactions subject to a higher rate as the best way for a visitor entering Canada to minimize conversion and transaction fee costs is just simply go to a Canadian bank and convert your US dollars there (but shop around and compare).
That is why I now have four bank accounts (well 5 if you count the joint account that they structured for me in Canada - identical to the account almcc described), so I can keep as much of my FREE banking while travelling abroad while avoiding any transaction fees (bankcards used in different places subjected to a fee), or transfer fees with easy access to my money (actually avoiding transfer fees) while using a different bank with more branches in greater locations.
Two of my accounts are from different credit unions, one savings and money market which no electronic transactions are used, and the other one is strictly a checking account where the debit card is used (they offered me $5 to open that account on an invite back in 1998 which I accepted) as I keep a minimum amount of what is needed in case someone hacks a server from a business to obtain my card info or if my account ever got hacked they would not obtain much as I have at least that much control.
Neither credit union bankcards have a widerange of unlimited free ATM transactions for me, they are only for a selected range of machines that can be used for free.
The third account is a major bank with nationwide branches thoughout the US, in which I learned back in 2001 that the last time I travelled in the states I almost resorted to doing a wire transfer from my credit union bank which would be a $30 fee (which I was reluctant on wanting to do) as I needed some more cash as I was in a win win situation on a sports wager and needed to obtain some more capital to hedge with an additional wager plus 3 point middle to possibly hit both wagers, but a friend had loaned me the funds instead and I paid him back in 4 hours after the loan and treated the whole family to dinner while celebrating as I paid a $65 tab, believe me I was more satisfied buying dinner for others versus some bank potentially profiting an additional $30 off me.
I found an old post back in March this year that is similar to this subject (how you'd handle money) and the changes I decided to make and adapt to when I stumbled into road blocks for the first time attempting to convert US dollars back in 2010.
The next post will elaborate on this topic even further as it is a copy of what I posted back on March 2013.