I have only put shrouds on threaded barrels myself, so I can't advise about the thread adapters, but I would assume this would be the cheapest option. If it were me, rather than pay to thread the barrel, I would consider selling the OE barrel and buying a shorter (8" bull or 12.5" tapered) threaded barrel from Dlask. Whichever you decide, I can recommend tacticool22.com and kineti-tech.com for the shrouds - both ship to Canada.
I seriously doubt you will notice any change in accuracy unless you replace the barrel.
I seriously doubt you will notice any change in accuracy unless you replace the barrel.