It's interesting that the pilots' actual blood / breath / urine alcohol readings have apparently not been made public as part of the charges. If they are indeed in excess of the UK legally prescribed limits (and presumably are), then both may be looking at up to 2 years imprisonment and /or a hefty fine. That is before TC throws the CDN book at them.
The news releases also state that both have now been suspended and have surrendered their passports. If this is suspension-without-pay (as a result of being formally charged by the authorities) they may be in for a very long haul. Such cases can take months to prepare / try in open Court, especially if a not-guilty plea is entered. Such charges are almost impossible to beat, unless there is a 'technicality' such as the testing method used or reliability of the equipment utilised on that particular day.
It's going to be a long, slow and ultimately very costly experience for them both. (On the upside, with their Air Transat experience, they'll be well-used to gross-overcrowding, lousy food and inhumane treatment commonly found in H.M. Prisons.
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