Hi there! Likewise, we moved apartments in the same building. I just kept the same street number address, but changed the apt/unit number:
so, as an example, one entry has 1234-56 My Road, City, Province 1a2 b3c
and then the other has 4321-56 My Street Road, City, Province 1a2 b3c
There is no need to write the building name. It is enough to write your address as if it were for Canada Post.
Every time I have applied to extend my visitor record, an address like the one above has been fine.