Lenders are required to verify that you can afford to pay the new mortgage payment and all additional expenses that come with home ownership.
You will need to provide confirmation of your income, such as a recent employment letter and paystubs from your employer, or your previous two years T1 General tax returns if you are self-employed.
The lender will also ask to see confirmation of your down payment funds and closing costs, in most cases this means 90 day history on the account(s) the funds are currently in. Gifted down payment will be acceptable in most cases.