Bear in mind some of the answers you are getting are likely based on a lot higher flow rate and pressure than used in a typical canister filter. Friction loss goes up with the SQUARE of the velocity, so twice the flow means 4 times the friction. So loss from (say) house water supply or sprinkler systems is a lot different than a low flow circulation pump.
I'm not saying it is not an issue, I think you might be very surprised. I just looked and my plumbed tank has three 90's on the intake, and five on each outflow (except one of the three has 2 45's vs 2 90's). That's a lot of turns, but honestly I do not see a noticeable drop in outflow vs. when I tested it in a sink with buckets. I'm sure there is some, but it was perfectly acceptable, and a LOT easier than using flexible tubes.
As mentioned -- PVC is cheap. It's no big deal to test, and I suspect you will find it works just fine.
But if flexible works for you, great.
Here's where my 90's went. This is looking UP toward the top of a 6' tank. Two canisters each go along each side to the two center braces as a spray bar, and the third is on the far right on this photo.
By using PVC everything is stationary and doesn't flop around.
This is a top view where they all go into the tank. Despite all that pipe, there's a small cover over one end, and no one notices the plumbing when looking at the tank.