Comment by hylaride
By that argument we should do that with everything. Maybe...with tariffs? /s
Doing that is more expensive and means we get us less for more - and we'd almost still rely on other countries for components and resources. All being equal, it is better to buy foreign goods cheaper and then have money leftover to focus on investing what you're good at. Canada is too small to economically fully design and build a modern plane, engines, missiles, radar, etc to compete with the US, China, etc. We certainly can't afford to do that with everything else, as well.
There are absolutely overriding strategic and security reasons you may want to do some of this anyways, but as a general rule we'd be far better diversifying our defence alliances (eg buying a mix from France, Korea, Japan, US, UK, etc) plus having something really good to offer said allies so we can be interdependent. Countries (including the US as we're learning) are not more powerful when they go it alone.
Protected industries almost always get lazy and noncompetitive. Canada is building our own version of the Type 26 frigate for almost double the cost per boat of Australia and the UK (which already ate the design costs!) despite the fact that we're going to be building the most of them so we should in theory scale cheaper. There are some reasons for that (they will be the most capable type 26's afloat), but it's mostly just because the government wants to subsidize Irving and east coast shipbuilders and there's no real scale or expertise because they literally can't market their work outside of Canada.
The argument is that naively looking at the price tags of domestic and foreign weapon systems doesn't tell you the true costs to the country. A dollar given to a foreign country costs much more than a dollar spent inside your own economy.
This is hardly even a novel or controversial point. Any defense spending expert will tell you this. Even that trendy Perun guy that reddit loves has made this precise point.