Can the client choose more than one target location? Additional cost?

As decided by the client at sign-up, we can backup to multiple locations if required but cost will increase accordingly.  Usually, we allocate Canadian clients to Canadian data centers and US clients to US data centers.  Note this is determined by the M365 tenant location which is selectable by the client, it cannot be done at a user-by-user level within M365.

What safeguards are in place to ensure OCP M365 backed-up data remains resilient? Do we duplicate or replicate the backed up data?

M365 keeps a duplicated copy of the data for availability in the platform, we are considered a tertiary, offsite, copy of the data. Our backup platform runs on Enterprise storage technology that is fully redundant and highly available in nature. We do not duplicate or replicate the backed-up data unless specifically requested. This follows the 3-2-1 methodology of 3 copies of data, in 2 different locations, 1 of which is offsite.