Bad form for the landlord, but perhaps "crazy" is overstating it. The landlord has little to lose by seeking to accommodate the tenant's request.
Worst case scenario: The tenant proffers the false document to the IRCC and the IRCC catches on to the truth. So what? For the tenant, a big problem. Caught in a lie in an immigration application. Serious repercussions. But, for the landlord, what fallout? I submit absolutely nothing. Is the IRCC going to seek to bring criminal charges against the L/L? I hardly think so. And what would be the charge? Some kind of criminal conspiracy charge? Conspiring with the tenant to deceive the IRCC? Is that a matter with which the criminal law is concerned? Even if so, would any regional Crown ever approve a charge like that? Kinda' silly to think that the L/L has any real exposure here to negative consequences. On top of that, the IRCC is quite welcoming of criminals into Canada, so why get on a high horse over some L/L who simply wanted to do a tenant a favour?
Yes, whether or not the L/L was aware of the intended use of the false document, I think the L/L's heart was probably in the right place, albeit a bit misguided. No different than a family physician who gets asked by a patient to write a letter supporting the patent's CPP disability application, or their application for a disabled parking pass, etc. Many times they don't believe in the application, but want to appear as supportive to their patient.
As for the comment that the L/L was crazy for altering a "legal" document (and legal rather than "semi-legal" would be correct), again, a bit of a stretch. First of all, no document was "altered", if I understand the facts. Rather, an entirely new document was created. The landlord and tenant were free to create any document upon which they might agree. Can any stranger to the transaction be heard to complain about their conduct? That would be so even if they did, in fact, "alter" the original document. Who has the right to condemn their conduct? No one. However, if the intent is to use that document to deceive some third party (such as the IRCC), then that third party has the right to complain. But, as noted, will the IRCC come back at the landlord? I can guarantee that won't happen.