I've always found it best to convert to Canadian dollars at a US bank before going over there.

Or check with your bank if you can get the same preferred rate at an ATM in Canada, but beware the cost of the transaction fees

and I have found the USD is pretty much universally accepted, but if you want to be sure why don't you just hit an ATM for the exact amount of your date. You will get the best exchange rate and you won't be risking any awkward moments that might result in not having any Canadian dollars.

1$ USd = 1.37 Cad

The exchange rate should not be that bad.

if you pay cdn rate in US $ its like giving a 20% ti

The best exchange rates are sometimes found at the Niagara casinos!

In Canada independent prostitues are legal for the lady BUT the guy can be arrested.  I was in NB just after the prostitution law was struck down by the Canadian Supreme Court.  The lady I met was laughing at me being careful about our date.  It felt good for the brief amount of time the law was struck down.  But afterwards the then conservative government wrote a new law making it illegal for the Johns (guy).
Have fun

In general the CA side of the boarder is very happy to take US$ but it used to be pretty much a 1:1 rate in the stores (never hobbyed there). That said, when I was getting up there much it was much closer to a parity rate 10 cent or so. Now you might get a differential from the girls without changing money -- whether or not it's a better deal or not....

I know some of the banks up there used to provide currency exchange for, at least some of, their customers without an exchange fee (probably still a mark up applied to the published rate but...). If that's still the case the girls might be able to convert at better rates than you so they might offer a better deal.

I have played in many different countries, and while they were generally willing to take US $, I can't think of a time when I didn't get a better rate with the local currency than with US $. With the US $ now being worth about 40% more than the Canadian $, my fear would be that upon arrival the lady would accept my US $ at par.  Just hit the local ATM upon arrival, it's not difficult.  (Plus, you can't blame the ladies for preferring the local currency...as they will have an expense when they exchange it, and in some countries having US currency can cause them all sorts of problems... though not in Canada.)