I haven't found any information on which exams are required
Article 8 of the Aircrew Regulation confers a discretionary power on member states to grant Part-FCL licences, ratings, and certificates to holders of equivalent ICAO privileges subject to a basic set of conditions given in Annex III, parts B and C, of the
Aircrew Regulation. The required exam papers are air law and human performance. Note there is no requirement for an FRTOL to be obtained however one is required to operate a UK aircraft radio.
Part C of Annex III establishes minimum requirements for the conversion of aircraft ratings and introduces a need to be "in current flying practice." This requirement is repeated on the CAA page you gave for
Online Applications, in the last section 'converting from a third-country ICAO-compliant licence,' but it is not defined by UK or EU regulations or rules. If someone has knowledge of its practical definition then please post a comment. If not "in current flying practice" for a given rating then it may still be endorsed in the Part-FCL licence but will be restricted to Canadian aircraft. The CAR 401.05(2)(b) recency requirements made for carrying passengers are irrelevant.
It is important that your TC medical and booklet remain valid during the application process. The UK CAA website lists TCCA CAMEs
here should revalidation in GB be needed. UK Information Notice
2017/021 (Verification of Third Country ICAO Licences) in para 3.5 states: "The CAA will not recognise an expired ICAO licence or medical certificate in any circumstance."
Only include
certified copies of relevant logbook pages, i.e. those showing 100 hours of flight time as a pilot, any additional requirements necessitated by subpart H of Part-FCL (e.g. FCL.710), 100 hours of flight time in each aeroplane class whose rating is sought, etc. A certified copy of page 1 of your booklet should suffice in lieu of a passport. The radiotelephony examiner conducting your practical test for a UK FRTOL, equivalent to Industry Canada's ROC-A, is empowered to assess whether your English language proficiency is at the expert level. The Course Completion Certificate will be completed and signed by the head of training at your approved training organisation.
You might also consider using a UK/EASA logbook to accommodate information not normally logged in Canada such as departure and arrival times, number of landings and takeoffs, how many beers you're owed, etc.
Would it be a problem if I complete the theory at a different ATO than the flying bit?
See the response from Whopity in this recent thread:
http://www.pprune.org/private-flying...ml#post9562360