Thank you to all who responded to my travel medical insurance question. We are Canadians travelling to U.S. for 7 days. I just obtained insurance from Bestquotetravelinsurance.ca.
You can purchase pre existing condition insurance and choose the option of stability period that works for you. We purchased 7 day stability as all conditions were stable but Synthroid medication for thyroid had changed recently. The cost of the policy was approx $75 for a 63 year old.
Hopefully we won't need any of this!