Read and re-read Tod's answer. That's how a METV works. To get the most out of the METV (almost a full 9 months), you have to enter the country as soon as you get the visa.
If you don't enter right away, you're wasting away your METV. Might as well have gotten a SETV and used two visa exempts stamps instead (8 months total).
That's why you get a cheap $50 Air Asia online, within the 54 days even (since the airline might not know about the 45-day change, or even about extensions), and you show them that ticket, and not your other return ticket. You can use that cheap ticket, or not use it at all.
Had you entered everything correctly, you would have probably been rejected for the overstay. An embassy will not approve a visa for someone planning on overstaying.
You're recommending this, but have you ever used one of these? And how recently?
Just buy a $50 Air Asia ticket to a neighbouring country. Paying $50 instead of $15 for a sketchy service, and not risk losing your expensive flight and trip.
Don't change your expensive ticket. Just buy a cheap Air Asia ticket for $50 to a neighbouring country, and show that. Use it or don't use it. I wouldn't risk losing your flight by using one of those onward ticket sites.
How did you apply for a Non-Immigrant B e-visa from Canada? You had all the many required documents from your job, and you provided these to them electronically? I know it's possible to provide physical documents at embassy in Canada, but not electronic documents for a "Non-Immigrant B evisa."