Huuuh, Whats up doc?
In my humble opinion, the H&R Block guy is not quite right. I think the angle he might be advising you on is that you would remain a UK national, and not taking the OECD route. Which is what I would ultimately suggest.
All the answer to your questions are answered on the Seafarer Tax Page as found on the main site, although granted, sometime it seems to be buried in there. But to cover your particular questions here, I answer your queries in Italics...
Now is that 6 months in one go, or cumulatively throughout the year? - Not necessarily, there is a tremendous leeway by CRA, as far as I can tell, for break and time off periods. Time inside the country or not may not be voiding your claim.
Is it only applicable to those in the Oil & Gas sector? - For all intent and purposes, the answer is yes to this questions, as it regards us seafarers. Farming, construction and engineering are also included in the scope of application, but basically its a very narrow criteria for say a few big O&G companies and constructions types like SNC Lavalin and such.
Does it depend on Flag registry? Not really, the onus is on the company that issues you the paycheck, and where they are based and what type of work they generally do (O&G, Farming, Engineering etc.).
I work in the yachting sector, as there was more money to be had than slogging in the North Sea for months on end. I get 4 months at home, which I am not so overjoyed with, but considering the time it affords me at home with loved ones, is something I can live with. The brits still cant shake those shitty contracts !
I am not applying for residency just yet, as currently I'm not paying tax to the UK. I don't want to make a decision to move to Canada only to find that I'm going to be screwed for tax for the rest of my working career.
I think your strategy should be to reside in Canada but not be a resident of Canada, I am not sure exactly what visas you need for this, while remaining a UK citizen. I believe this is possible for you at least in the short term, 3-5 years, you would just be a frequent visitors, once or twice a year.
There is no tax breaks for Canadian seafarers (citizen and resident) working internationally, that's the bottom line. But that's not to say that there isn't legal way around, that would fit your wishes to reside in Canada. Unfortunately, to date, no expert in this field has been identified in this field.
I'm sorry this situation in Canada sucks. But our government leaders just can't seem to get their heads out of their asses when it comes to maritime matters.
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