Be aware that it's geo -magnetic latitude we are talking about here, not "true" latitude...or put very simply your distance from the magnetic North Pole. The "worse" routes for Dose Rates are those across Northern Canada. On the Siberian routes you tend to get lower rates but for longer......
(edited to add
FWIW, three or four years back I calculated my exposure for all my flights, ( B744, European based, flying a mix of Transatlantic, African and Far East sectors) for a year, using the CARI program..My exposure to galactic cosmic radiation for the year was, from memory, around 5 mSv, nowhere near the European limit of 20 mSv mentioned elsewhere, however the version of CARI did not calculate exposure to flare events.
As far as I'm aware, IMHO, the jury is still out on this - sadly plenty of people who never go near an aircraft die of cancer, very roughly 30% of the general population in the UK, so personally I'm not convinced there is, as yet, a widespread radition induced problem. However with aircraft like the 777 and the Airbuses climbing straight up to FL350 plus after takeoff and the bizjet guys cruise around at FL450 plus maybe the stats will begin to show something a few years down the road.
OTOH we could all ( well Brits anyway) opt to be Earthbound and instead of flying, struggle daily with the endless commute around the M25, breathing in all those lovely fumes, suffering raised blood pressure and having an fairly good chance of dying in a car crash - it's up to you!