First, someone in the company must have encountered these temperatures before. Ask them.
Also Environment Canada should have historical records that will help you decide the level of protection you will need and a reasonable temperature value.
You, and your customer will have to come to an agreement on the level of protection required and how to achieve it.
"If we all worked on the assumption that what is accepted as true is really true, there would be little hope of advance." -- Orville Wright
We have adopted new policies. Please read each one carefully.