> How do all these new polar routes affect the workload of the people staffing our Arctic radar stations, if at all?

If you are referring to the people doing the radio work, through the magic of HF radio they sit in a nice warm office in Ontario, Canada.

I doubt it will increase their workload much as its not a busy route and there's not much ATC to do given the sparse nature of the region. Its more of a monitoring service per-se.

P.S. They are not "new" routes. They've been around for decades, just lost popularity due to better options.

No. Civilian aircraft have transponders on. They can be identified easily.

If you mean en route radars, those should not be affected. Those are big rotators that work the same, 24x7, regardless of how many planes are in the area of the coverage.