I'm also Canadian (Montreal) and the first time I went to BA I did not do any research… and was therefore gouged at the ATM.
I'm with CIBC in Canada. I paid $5 CDN per ATM transaction to CIBC plus approximately $5 CDN in Argentinian bank fees. If I recall (this was two years ago), the daily withdrawal limit was somewhere around $1000 pesos, so a minimum of 10% in fees. Add to that that the CDN is worth at 0.9 USD right now and that you also pay a couple of percents to change the money, so maybe .88. It makes Buenos Aires very, very expensive.
All of this to say that you should avoid the ATMs.
I was also a solo female traveler. At first I found Florida creepy but now I'm totally comfortable with it. I don't change too much money at any one time. I basically go to the same place (a travel agent) every Monday and change $200 USD, which I live on for the week.