A few things to bear in mind about the CPL skills test you will have to do:
1) UK wx - obviously can't be too bad and need some basic minima for the upper air work and navigation stuff.
2) Navigation - you say you know how to fly the plane etc - I assume you have commercial experience in the US. I am similar to you, - comm experience in Canada. Now, the thing is, if you're like me, you will have a ton of time under IFR flight plans, cleared dct, following airways or GPS etc. When was the last time you got out a map, drew a line and used a stop watch / DR technique with reference to the ground below? For me it was a LONG time ago. The UK (and Europe) can look like an unidentifiable blur of little villages and winding roads from the air - this part of the test will be my weak area - could also be yours?
3) Air work - sure we can fly the plane on a daily basis - but again I can't recall (since my Canadian CPL test) the last time I did procedural airwork - time turns, unusual attitudes (ok do that in the IFR recurrent), glides, different config stalls etc etc. Something more I need to polish up on.
4) UK R/T work - quite different from the US/Canada. Things like types of ground agency (a/g, information, etc) MATZ agencies, FIS regions, etc etc and all stuff being done on QNH/QFE including VDF procedures.
Just some stuff to think about in the time frame it will take you to do the CPL test. I am allowing myself up to 10 hours, but hope to do it in less - just very hard to tell.