Can my portal search more than one flight supplier at the same time so my customer sees the cheapest fare?

Yes, a portal can search several flight sources at once and put the results together into a single list, so your customer compares fares in one place instead of you checking each supplier by hand. The search goes out to every source you have switched on, the replies come back, and duplicate flights are merged so the same journey does not appear twice at different prices.

The honest limit is speed and coverage. Every extra source you add makes the search a little slower, because the page can only finish once the slower suppliers have answered, and a source that is having a bad day can time out and simply be left out of that search. Coverage also varies, since one supplier may have a fare on a route that another does not carry at all, so more sources usually means better prices but never a guarantee of the lowest fare in the market.

How many sources you can run, and whether you can set an order of preference so one supplier is chosen when two fares match, depends on your plan and on what each supplier allows in their contract with you. Some suppliers are happy to sit alongside others, and some ask to be the only source on certain routes, so it is worth reading that part of the agreement rather than assuming.

If fares matter more to you than search speed, start with two sources, watch how long your searches take and how often each supplier wins the sale, and add a third only once you are happy with the results.