There are a number of facets to your question.

I gather that what you are saying is this: "I will need to borrow money to pay for the trip. As long as I have to do that, I might as well open a credit card account that will give me the most benefits when I buy the ticket."

Let me step through this one aspect at a time.

One possibility - which I don't think you were proposing, and would be hard to do - is to get the ticket from frequent flier miles that you get as a signup bonus for the card. No card gives enough miles for a round-trip ticket of that distance. It is possible you might get a signup bonus of enough miles for a one-way ticket, IF the associated airline has availability. But you would need to get the card and meet the spending requirement, then have the points posted, and then find award availability, all in a fairly short time.

Moving on, you can get credit cards that will give both bonus points when you buy a ticket on that airline and flight benfits, such as a free checked bag, priority boarding, and lounge passes. I don't sense that the non-monetary benefits are that useful to you, and you usually get one free checked bag on international flights anyway. If the bonus you get is in airline miles, you would have to accrue enough miles to actually get an award of some sort. That might not be so hard, since you'll get a nice chunk from the flight itself, but you have to know what airline you'll be flying on.

The suggestion that stands out to me is to get the Chase Sapphire Preferred card. After you spend $3000 in the first three months, you get 40,000 bonus points. These can be redeemed for $500 toward your ticket. When you buy the ticket, you will get double points, as well as double points for other travel-related items such as hotels, taxis, etc., and also for restaurants. These points can at worse be redeemed for 1 cent each in cash.

The Chase points post quickly once you meet the $3000 spending requirement. If you have trouble meeting that quickly, there are a wide variety of strategies, but two that might work are (a) make a large one-time payment against your cable and/or wireless bill and (b) find a close friend or relative who will use your card to charge on, and pay in in cash to pay the bill.

(Note, if you use this strategy, to get the $500 off the ticket, you have to book it through the Chase Ultimate Rewards website, but you will get the same prices as on any other site.)

The only downside to this is that you have to meet the credit requirements. If you are declined, you can call Chase and they will often reconsider, especially if you ask for a smaller credit line. They gave me a $25,000 credit line initially, which was vastly more than I needed.

Who knows, the $500 might even keep you from having to carry a balance on the card for the trip.

A related suggestion, if you find a fare you like, I would book it. It might be tempting to wait so that you pay interest on the unpaid balance longer, but you'd feel really bad if you saved $10 in interest and the fare went up $100.