Is it legal to have digital currency expire in canada?

You clearly don't understand what those words mean.

A gift card, even if it's an online form, is not a digital currency. It's a credit, based on an actual currency. And yes, credits and gift cards can expire, and legally.

That would assume that Canada has some form of recognized digital currency.

Hint: bitcoin doesn't count.

The best thing you can do is read the game's terms of service - which you are supposed to do before signing up with the game or whatever, and you're supposed to understand it. It likely talks in the terms about you agreeing to crap going away - simply by signing up, you agree.

See, here's what it says for the wow game:

YOU HEREBY AGREE TO DEFEND, INDEMNIFY AND HOLD HARMLESS BLIZZARD, ITS PARENT, SUBSIDIARIES AND AFFILIATES, FROM AND AGAINST ANY CLAIM, LIABILITY, INJURY, DAMAGE, LOSS OR EXPENSE

http://us.blizzard.com/en-us/company/legal/wow_tou...

WOW can delete my account and anything I might have bought simply because I agreed they could.

You might want to add and explain what's happening instead of demanding citations.

Do your own research.

Please use citations.