what is the max wire gauge for In-Ceiling Speakers

If you use banana plugs, it would be the limit on the plug.

@jgatie thanks, good point. I wonder what better raw wire or banana plug

https://support.sonos.com/s/article/4764?language=en_US

Distance is a big factor.  Also make sure the wire you get is rated for in wall use.

I prefer banana plugs and reasonably sized wire. If you go with over-sized or stiff wire a short piece of reasonable size and flexibility helps either connection method.

Fat wire directly into the Amp’s jacks is begging for a broken jack.

Too small wire hurts the sound, to fat is just wasted money.

@Stanley_4 thanks

I am thinking 14gauge . I have to go about 30 ft
I am thinking something like this
https://www.mediabridgeproducts.com/product/4-conductor-speaker-wire-99-oxygen-free-copper-etl-listed-cl2-rated-for-in-wall-use-14-gauge-100-feet/

although this is out of stock

14 should be fine, more than big enough to supply full power to the speakers and small enough to be flexible.

Your link was to four conductor cable, that can work if you run to the first speaker and terminate one pair there while taking the cable to the other speaker and terminating the other pair there. That leaves the first pair unused on the run to the second speaker.

If your locations would be better with individual runs to each speaker single-pair wire would save money.

Make sure to mark both ends of the wires with permanent tags or you or the next guy will have to puzzle out just what is going on.

What I have done is strip an extra foot of wire at the amp end and split the pairs to make the pairing very obvious. A few pieces of shrink tube will make the split both pretty and permanent.

Most 4-conductor wire is color coded.

A common scheme is:

Red: R(+)

Black: R(-)

White: L(+)

Green: L(-)

Two conductor wire should have some sort of scheme to identify the conductors. Sometimes this is very subtle, such as a very small ridge or printing. Other schemes are more obvious, such as a color stripe, larger ridges, or wire plating.

Pick a scheme and stick to it.

#12 wire is usually the largest that will comfortably fit terminals, but in my opinion this starts to get unwieldly. #14 is much friendlier. Stranded is more appropriate for audio than solid wire. However, check to make sure because I’ve seen some speaker terminals (on speakers) that will not accept #12.