Here's my 2 cents based on 25 years as a mortgage broker.
Mortgage "Fixed rates" are NOT based on the Bank of Canada. They are based on the similar Term bond market. As has been said earlier here, the Bank of Canada rate is an overnight rate and in a normal market can be changed about every 6 weeks. That said, and as we have seen, it can be changed at the will of the BoC and needs of the country's economy.
If an investor wants to place their money somewhere for an extended period of time with a known interest income, their two main options are Mortgages or Bonds. Mortgages are more risky and require more work (monthly payments, record keeping, sending statements, chasing late payments, potential defaults,...). The investor considering mortgages therefore considers the current bond yields in, world wide markets, and adds a premium for the work and risk involved in mortgage lending. Keep in mind that much of the mortgage lending in Canada is not balance sheet lending, (does not come from money the 'banks' have on hand). The bulk is from insured Mortgage Back Securities (MBS) and a surprising amount comes from non-Canadian sources. Those MBS portfolios can be quite large, $100 million $200 million or more. It's those investors who drive the mortgage rates, not Ottawa.
Because there are various sources and investors each MBS portfolio may have different requirements and rates depending on the restrictions that the investor requires. Some portfolios may require a lower return but only offer a reduced feature product with fewer services (e.g. no branch network). This is why you will see so many different mortgage interest rates on the internet. One of the most the popular lenders has as many as 32 rate buckets for just their 5 year Terms. The rate can vary with: percentage of income used to qualify, credit score, property type, Loan to Value ratio, whether a purchase or a refinance,..... For example, a purchase with less that 20% down can usually get that lender's lowest rate, Under 65% can also attract that low rate, 65% to70% is a bit higher, 70% to 75% is a bit higher, and 75% to 80% is higher yet.
Also be watchful for what each lender's "Prime" rate is. They're not all the same. TD is typically 0.15% higher than the common Prime.