Your rolls of commemorative silver coins are probably worth around 2.5 to 2.8 times face value, depending on the dealer and the precise condition of the coins. I got a nice roll of original bank-wrapped 25 cent lynxes for $25 a decade ago, and the last time I checked, they hadn't gone up in value (like nearly any Canadian commemorative coin from 1960 onward). The 1970 nickel is a better date and commands a premium, which can vary greatly depending on the precise condition of the coins. For example, if they are in the exact same condition they were in when they left the mint, they could be worth a couple of bucks, but if they have any blemish, gray patches (indicating circulation), etc., they would be worth much less.
When the GST was implemented in 1991, it almost killed the walk-in coin industry in Canada, because who would want to pay 13% tax (plus dealer's mark-up) on something that they may have considered an investment? The government might have made some concessions since then, but the Canadian market still appears to be at nearly the same levels it was at 10-15 years ago. Anyone want to buy some Montreal Olympics silver commemoratives for face value?
Finally, while you're in Montreal, even if you don't want to sell your coins, you might want to pick up a copy of Canadian Coin News to get a feel for the coin market in Canada. Here is a list of dealers in the Montreal area that carry this publication:
http://www.canadiancoinnews.ca/nushop.html#qu