The first thing I'd say is - Don't give up yet. It can be a lot of "fun" and very satisfying to fight against the big boys and survive. Makes a change from just building your own mega-airline and somewhat more relevant to the real world. In another game the biggest player out there moved into my base when I was just very small and I managed to survive and am now more than twice his size at that base and am beating him on nearly every route. There were six of us small guys and the others all gave up very quickly which made it somewhat easier for me, but was a bit disappointing too.
I'm no expert this is what I did to survive. Llooking at your airline I'd make these points:
1) You're still VERY small (20 aircraft) all leased. Get BIG as fast as you can (I know, easier said than done).
2) You have three fleet types comprising only 20 aircraft. It's probably too late to change plans now but can't the Dash 8 Q400's do most things the E170's can? Or vice-versa?
3) If you must use E170 series, really try to avoid the 170/175/190 and stick to the 195's if possible - their economics are much better. Also, avoid the LR and AR models when you can. If you need that sort of range for a route then it's probably not suited to an E-jet and, if not, you're just wasing fuel. You really MUST make three round trips per day with each one. Four would be better.
4) Going transatlantic with a single 767 at this point may have been a mistake, although I can't see the figures for that aircraft - maybe it's making loads of money. You need to either get rid of it or get more 767's ASAP. I notice it's quite old - the maintenance will be HUGE for such a small company.
The big competitor is NOT going to go away - he's way too big and can afford to make a loss a lot longer than you can BUT...
With your smaller aircraft you should be able to command a few of the routes he's moved into. e.g. 5 x daily with your E195 will always beat 3x daily with his A320 with about the same number of seats. The small aircraft are a GOOD idea in general. If you survive long enough, your E195's should allow you to beat him on most of the shortish routes eventually.
1) I'd pick a few key short-haul routes and make them yours. Let the rest go (for now). Be ruthless - if it's making a loss, chop it NOW and hit him somewhere else. Choose ones you can fly at least 4 or more times daily without over-supplying and they should make money at least. The competitor is much more likely to go for the "easy" picks from your routes unless he's being bloody-minded or just wants the challenge. Don't be afraid of downsizing - that's how I survived when I was under attack.
2) If you can't get rid of the 767, make sure it's making absolutely as much profit as possible. Can you tweak the schedule to get in two or even three domestic flights? YUL-LIS is quite a short flight. I apologise if you've already done that.
3) Be careful with your slots - they're HUGELY expensive in this game. When you chop routes (as above) be very sure to re-use the slots before you lose them. Also, make sure you don't spend all your cash (if you have any) on slots. You need more aircraft NOW.
4) Have fun and rise to the challenge.
Remember, he can only ever have 70 aircraft at that base so, eventually, he'll run out of options and THAT's when you can fight back and kick his ass!