Porting Mortgage

Depending on your mortgage is Close or Open, most people have a Closed mortgage to get a better rate, you will need to check this first (If you're unsure, simply login to the bank account and you should see the details). If you indeed have a Closed mortgage, you will have a penalty and you should consult BMO for an accurate amount, and you can ask them about borrowing more. Usually, your lawyer should take care of all the paperwork for you.

I'm not too sure why you will have 2 mortgages on the same property?

The process of porting a mortgage is essentially moving your current mortgage to your new home. No, there isn't any penalty as you aren't breaking your current mortgage. There are fees though as the mortgage has to be discharged from your current home and then registered again at your new home. If you want to borrow more as you are buying a more expensive home you can. That is where the term "blend and extend" is used. In essence, the mortgage amount that is ported is blended with a new mortgage amount. You will not have two mortgages on the property.

Here is a link that helps to explain it: https://altrua.ca/porting-mortgage/

In periods of increasing interest rates there will be more attention paid to porting mortgages. Also understand that when porting a mortgage you will need to go through the mortgage approval process again as the lender will need to make sure that the home that you are porting the mortgage to is lendable.