The sale does not end the tenancy. You are buying the suite and the agreement that comes with it, so read the agreement before you offer.
This surprises buyers every year. A tenancy does not end because the property changed hands — on possession you step into the landlord's position under the existing agreement. A fixed-term lease generally runs to its end date. A month-to-month arrangement continues until it is properly ended, and ending one requires the correct written notice under Alberta's Residential Tenancies Act. Confirm the current notice requirements, or get advice, before you build a plan around a date.
The security deposit and the interest owing on it also have to be accounted for at closing. Make sure your lawyer knows there is a tenant.
Two things are being sold here: a property and a contract. Buyers read the property carefully and the contract not at all.
If you intend to live in the suite yourself, or to renovate it, that intention has to be reconciled with the tenancy well before you write the offer — not negotiated afterwards. If you intend to keep the tenant, introduce yourself early and get the arrangement onto your own paperwork.
See also: Calgary suited homes → and how lenders treat suite income →.