That's not how a home equity line of credit(HELOC) works in Canada. You cannot get a HELOC to buy a house from scratch. HELOC is essentially a loan you get against the equity you already have in a house.
Let's say you bought a home for 500K, where 450K was your mortgage and 50K was your down payment.
Few years down the line, let's say the valuation went up and the house is now worth 700K. And you were also able to repay further 50K of your mortgage. So now you owe the bank 400K.
Now HELOC allows you to draw your equity upto 80% of the home's worth. So 80% of 700K is 560K. Out of this, you still owe the bank 400K. So with this formula, you could get a loan for upto 160K at very low interest rates. People usually take out HELOCs for things like renovation, or buying another house, or simply to invest, as HELOCs have very low interests compared to personal loan. For example, right now you could get a HELOC at as little as 3-4% per annum, and if invested wisely, you could earn 7-10% easily. So you are net in profit.