Lets assume that the only cost associated with covid is lost work. So lets weight death rate by age group and years to retirement i.e. if you're in the 50-59 age group you have a 1.3 percent death rate and we'll say 10 years till retirement, 20-29 0.2% and 40 years (we'll exclude people from 60 up as they obviously contribute nothing to society and their deaths are meaningless especially in a economic sense /s). We'll ignore age distribution as we're talking about Canada which has a population pyramid which is pretty much square accross ages 10-60 (similiar to US FYI).

So as a napkin calculation how many normalised years of lost labour do we have from the deaths... 0.13 years from the 50-59 year olds, 40-49 0.08, 30-39 0.06, 20-29 0.08, 10-19 0.1, for a total of 0.45 years of lost labour from deaths if the whole country caught covid.

In a world were all economic activity can be turned on and off like a lightswitch it would make economic sense for Canada to flick that switch and leave it off for up to 5 months (of absolutely zero economic activity which is not the actual level of lockdown as essentials still run) to irradicate covid, from the impact of deaths on work produced alone.

So yes as a general rule I would argue that locking down entire countries can make great economic sense if you can lower your death rate (say by using the time where covid spread is reduced by rolling out a vacine that would reduce the lost time to 0.0045 years if everyone got it). Though of course you'd need to get into the nitty gritty of stunted business growth and if killing off 8% of people over 60 is a good way to reduce taxes needed to support them to have a definitive answer.

NB: I'll add that I'm replying to your question on the economic sense. Personally I find reducing the pandemic to this view deplorable but as some do argue it I thought I'd argue the countercase along those lines. I.E. Even if you're a heartless bastard only interested in money you should still be enforcing strict controls until your population is aproaching as vaccinated as it's going to get.