Thanks for your clarification. Don't feel at fault for having this coverage. I know of many who got sold into whole life or UL policies, including myself at about your age. Like you I finally realized it was not a good deal for me while it is a very good (and profitable) deal for the salesperson and the insurance company. The insurance business has been around for a long time, so the selling methods are refined and convincing. It can be difficult to argue with a well polished, knowledgeable salesperson who 'wants to help make sure your family is looked after'. They aren't crooks, they are sellling you a product and they are earning a living, but they aren't giving you the best value for your money - that is up to you.
With a wife and child you definately want insurance coverage, sufficient that they would not face undue hardship if you were to die. But you can get that coverage for much less than $300/mo. Check out https://www.term4sale.ca/ to get some idea of the prices. You could be paying closer to $45/mo for $300k of coverage (b.1988, term to age 70).
The general consensus is to keep your life insurance and investment products separate - products that mix the two (i.e. UL, WL) benefit the company not you. Buy term life insurance to insure youreslf and buy investments to invest.
I suspect the 20 year paid up policy that you mentioned is an 'illustrative' case which depends on certain future investment performance (or a reduced coverage amount), i.e. it is not guaranteed at $300k. Remember also that $300k in 20 years may not be much coverage net of inflation.
You may want to get some term life estimates online and then tell your agent you want to change to term life for you and your wife. Be prepared for some compelling arguments for not changing, but remember it is +$200/mo of your hard earned after-tax money at stake. If they won't help, you have to be prepared to cancel your policy - after getting term coverage elsewhere. Or you may just want to line up term insurance elsewhere and then cancel your UL outright. It depends on your past relationship with the agent.
Do you know whether your employer offers a group term life plan? They sometimes have good pricing.