You are wrong, this letter comes with the sponsor approval, it is not the invitation to apply
As the matter of fact, midi clearly states on their website:
If IRCC finds your sponsorship application is eligible, you will be invited to
continue the process by submitting an undertaking application to Ministère de l’Immigration, de la Diversité et de l’Inclusion (MIDI)
You haven’t even applied for IRCC at this point, therefore you don’t have this letter, do what you want, but in a week you will see I’m right, good luck