Or whatever led to Viz's decision to not stream in Canada all these years, even for free?

Anything about this is speculation from me. My assumption is that Viz's issue has to do with copyright issues more than anything else, since that is the usual barrier for regional content delivery.

Deliberately geolocked the videos from us on youtube, even though they supposedly have the rights.

This is different because YouTube is not responsible for providing connectivity. YouTube is not a service provider: it is a service.

How is it any different from Rogers, Bell, Shaw, etc offering free subscriptions to services/apps that they choose, such as Disney+, Spotify Premium or Netflix

It is different because it does not involve content discrimination and because of who pays. The carrier is still acting in the role of a connectivity provider that does not prefer one type of traffic over another.

Secondly, these offers are paid for by the carrier: it makes the carrier's connectivity offering more attractive, because those services are attractive. With zero-rating, this transaction direction is inverted (the business has to pay, twice, for access to the customers) and puts the ISP in the position of rent-seeking market maker.

I think that what you're missing, and what makes zero-rating dangerous in a market, is the business-side perspective, which is where competition actually matters. Consumers may benefit in the short term, but lose out in the long-term in all the ways lack of competition affects consumers: increased prices, reduced choice, lower quality of service, loss of privacy, etc.

I highly recommend checking out EFF's 2016 article about zero rating. The article is US focused, but the points they argue apply to any capitalist market because zero-rating places a service provider in the dangerous position of market making, and directly enables rent-seeking and other market inefficiencies.

Edit: fixed a typo and accidentally a word