how long is a multiple-entry canadian visitor visa valid for? maximum validity?

Answer 1

Sorry you question is not 100% clear.

If you have a Multiple -entry visa in your passport , the termination date is always listed.The usual is either 12 months for the first time or 5 years.
Once you arrive in Canada the immigration officer will tell you the actual amount of time you can stay in Canada.They will usuallly allow you to stay 3 months . Please note that you cannnot stay more than six months a year in Canada as visitor. That is the total amount of days each year.