There are various reasons why an online casino in Canada accepting MasterCard could block your account. Some of these include:-
Incorrect login information, or too many incorrect attempts to logon
The online casino not being able to verify your identity or financial information
Suspicion of fraud on your account
Attempts to open more than one account with an online casino
If your account is blocked, which can also mean that the funds in your account can be frozen, it would be best to contact the online casino’s customer services.