Can my landlord force me to close windows in my overheated…

This is a ridiculous letter because you are not in substantial breach of your lease at all. You aren't in breach of your lease.

If you cause the pipes to freeze then you would have to pay for the damages. That's all you agreed to and that's all you're liable for.

You can tell the landlord that you have received legal information and this is what you've been told and on top of that if they don't want you to have to open the windows they need to stop overheating your unit because you have the right to peaceful enjoyment of the home. By putting this provision in the lease we can see that they already know that overheating is a problem.

If your landlord deprives you of the right to peaceful enjoyment of your home either because you are overheated or because they are harassing you with threats of eviction you can tell them that you will bringing an application to the residential tenancies dispute resolution services for an order requiring them to grant you peaceful enjoyment of your home and for a rent abatement for the times when they have deprived you of that rate. Here's a link to their contact information so you can discuss this with them as well:

https://www.alberta.ca/contact-rtdrs.aspx

Does that help as a starting point?