USA, Canada / Shipping personal possessions from US to Poland [11]

Your best bet is to contact one of the Polish Travel Agencies. If you can't find any (I know there are plenty in CT area) then let me know, I'll look them up for you. I am in Boston and around here our Polish Travel Agencies take care of things like that for you. They will know best and most reliable businesses. Don't use Uhaul or one of those large ones... they don't do enough of this type of business so they will charge you arm and leg and will simply sub-out most of the work to some other agency.

USA, Canada / Shipping books / package to Poland from US [15]

Like AdamK said, find a Polish Store... in my area (Boston) it would be done in one of our many Polish Travel Agencies. They use private reliable shippers that I've used for over 25 years with no problems at all.