ASRock B450M Steel Legend AM4 AMD Promontory B450 SATA 6Gb/s Micro ATX AMD Motherboard ($139.99 - $40 - $40 MIR = $49.99) [Newegg

Actual price 59.99+tax

Especially if you're sending from way outside Toronto, best to submit the form on the day you get the item, or the day after. Make sure you read and follow the MIR instructions carefully, and get it postmarked by the post office to be sure.

I did it years ago, and it did work, I got a cheque for the rebate amount about 2 months later.