Edinburgh transportation to Glasgow airport
 

I'll be in Edinburgh for a week but flying back to Toronto out of glasgow. The flight is around 8:30am, and I'd like to arrive at the airport about 3 hours in advance. It seems the buses and trains don't run that early? Does anyone have any suggestions? And if my only option is an airport taxi, does anyone have any trustworthy recommendations for a good company?

I'd go to Glasgow the night before; it's only about an hour from Edinburgh. If you really need to be at the airport at 5:30, I'd stay at an airport hotel.

Very difficult . As mimar says -- book the last night at a Glasgow airport hotel. Even if that means 'eating' the last night in pre-paid Edinburgh accommodations. You could travel to Glasgow after dinner so not lose any "Edinburgh time" at all.

I guess the only option (that would get me there three hours before the flight) would be an airport taxi?

You want to take a <i>taxi</i> from Edinburgh to GLA? You must be in a higher pay grade than I am . . . .

It might be cheaper to get a room at Glasgow airport the night before your flight.

Janisj-an airport taxi (I think)?? The quotes seem to all be around 90£. It's either that or I lose the $120 Cad on the accommodation I already have in Edinburgh + another $100+ Cad for a hotel in Glasgow. Unfortunately the city link us isn't quite early enough.

you don't need to pay $100 for a GLA hotel. and much less than £90. There are budget hotels at GLA.

You have to pay the $120 in Edinburgh in either case - but you won't get any benefit from it since you'll have to leave your hotel about 4 AM. I'd get a cheap hotel at GLA and take cheap public transport the evening before. You'll likely end up money ahead or a wash.

I'm at a bit of a loss why the OP thinks they need to be at Glasgow Airport three hours before the flight. Since the new security check hall was introduced a couple of years back it's never taken me more than ten minutes to go through. Getting to the airport for seven is perfectly doable.
The 5:15 Edinburgh bus gets in to Glasgow Buchanan Bus Station at 6:25 and a taxi to the airport from there cost about £15 and takes 15 minutes. Taxi's pick up from directly outside the bus station on Killermont Street.