How to upgrade only one marketplace?

I am selling on two marketplaces (Canada and USA) individually. I would like to upgrade only my Canadian store to the Professional plan. However, when going to upgrade I see that the option to upgrade only one store is disabled and it is showing that I must upgrade both. A few questions:

If I upgrade both do I have to pay 2 separate professional plan fees?

How can I upgrade just the Canadian store?

If I can not upgrade just one store how can I remove the United States store completely for now?