Not with the gift cards but here are some of your options:
A) Refer here: https://www.buybitcoinworldwide.com/canada/
Choose those options without the need for bank accounts. Basically you will pay with cash on those designated payment centers. Although you need to undergo KYC it's for your own advantage and the next time you will buy BTC, its now one-click.
B) If you are not comfortable with KYC, try to search for BTC sellers on your locals: https://bitcointalksearch.org/topic/canada-183337
C) You can also consider having a P2P exchange within the community on the Currency Exchange section and there might be willing to do transact with you without any hassle. USE ESCROW!
Question 3.) OK - so i've got a Canadian GC - i've bought some crypto. Which Casino should I go to? I'm looking at CryptoSlots - but open to opinion!
Aside from those - any other tips? I'm mostly looking to play slots or blackjack.
Most of the casinos you will find here with an active community are all good. It's now up to your own preferences. So yes, there might be a chance that you need to play at each sites before there will be a site that will pass your criteria.