I’m buying a house, very good deal, I can miss, but I still rent a house, can I cancel the contract just because I am buying my own house.

Talk to your landlord and see if you can work something out. I had to get out of a lease for the same reason and found a pool of replacement renters of which he chose one and let me out of my lease.

Or he may let you sub-let it for the remainder of your lease.