Is my landlord doing tax fraud ?

the landlord is within his rights to use the address as a mailing address.  But you would be unable to sign for any packages.  Also, it would not be wrong for you to return mail to sender as 'not living at this address'. But the landlord would find out and could make life difficult for you or not renew your lease.

At the end of the day, it makes no difference to you where his mail is sent and if he is doing tax fraud, he will be caught up sooner or later. It could just be that he needs a Canadian address for some things, and so, quite rightly, is using yours.

It would be very easy for the Government to check who lives at your address anyway, and he would find it difficult to prove that he did...

Yes and she they sound like they are Portuguese because only Portuguese people are this nasty corrupt 

You can make an anonymous call to Canada Revenue Agency at 1 (800) 959-8281 to report suspected tax fraud.

It's his house and he needs a Canadian address to receive Canadian mail, so why wouldn't he use HIS house as his Canadian address? The only thing that would be unreasonable is if he expects you to mail it to him in the U.S., at your expense.

It's completely up to you to take HIS mail to the post office and tell them that 'this person doesn't live here, I keep getting his mail'. When it's delivered, write on the outside 'wrong address, return to sender' and send it back into the mail system.

It's the easiest way to stop whatever illegal thing is going on. The only mail that's ok to deliver to your address is YOUR mail, not his.

Check with CRA.  If the landlord is NOT a Canadian citizen:  If the locations were reversed, the USA taxing authority would require you to send them 30% of each rent check. 

I don't think anyone but your landlord would know his motive. There could be legitimate reasons why he receives mail there. 

Regardless, of where he receives his mail, the government would not know what is in the mail or that he is collecting rent.