The Home Buyers' Plan lets you withdraw up to $60,000 from an RRSP tax-free for a down payment, but the Canada Revenue Agency requires you to repay it into your RRSP over the following years or the unpaid portion becomes taxable income. The FHSA is a separate account allowing $8,000 a year up to a $40,000 lifetime limit, and using both at once is allowed, provided you track each program's own schedule separately.
The order you draw from each account can matter more than the total amount available, since some lenders want to see funds seasoned in an account for a period before closing, and pulling from three sources at the last minute can raise questions during underwriting. Sorting out the sequence with your lender before you write an offer avoids a financing condition falling through over a documentation gap.
Treat each program as its own file with its own rules rather than one combined pool of money, and confirm the combination with your lender and the Canada Revenue Agency's own guidance before you rely on it. Get your hand-reviewed valuation from Joel Dyck.