USD Cheque - Mobile Deposit into BMO? - RedFlagDeals.com
You cannot mobile deposit a USD cheque to a USD account at BMO Canada, nor do BMO ATMs allow deposit of USD cheques. You can deposit it at any branch and wait 28 days for it to clear (slowest of any bank in Canada). Hopefully your branch would release some of the funds earlier if you have a good relationship and sufficient balance with them.
Source: forums.redflagdeals.com