No it isn’t possibke - you need a pair of ‘matching’ speakers, one each for the rear left and right Home Theatre channels. See this support link:

https://support.sonos.com/en-us/article/surround-sound-guidelines-and-limitations

Thanks very much for this answer Ken. I will get two of the Era 300s to complete the entire Arc + sub + Era 300 experience. On the installation front, I’ve been reading reviews this morning and one indicated a need for ethernet cable connections to fix a lag between the Arc and the Era 300s and sub (https://cybershack.com.au/reviews/sonos-era-300-as-rears-to-the-sonos-arc-superb-dolby-atmos-7-1-4-review/?unapproved=60193&moderation-hash=9d98285680f738e006005efc5e7695f2#comment-60193).

I'm just building a house at the moment with the Arc, sub and 2 Era 300s in the home theatre room. The Arc will be connected to the TV with an eArc HDMI cable. I wasn't planning on connecting any of the 4 Sonos speakers via ethernet, instead was planning on just relying on wifi connection (as I have for all my Sonos gear in the past). Based on the review, that could be a problem. Do others agree and, if so, should I provision an ethernet cable back to the main router, or is there some way of directly connecting the Arc, Era 300s and sub together? Thanks so much

That would be incorrect, no need for the cables, the Era 300s would connect to the Arc using a 5 GHz wireless channel. You could provision the cables if you wanted, but they are not necessary. 

I’m a wire freak. In my opinion wiring ARC to the network would be a good idea. Since you are building a new house install wires everywhere. You’ll be using multiple WiFi access points and these should be wired. Certainly, wire each TV and computer cluster.

If you really want to get out in front, run some optical fibers to major locations, such as TV’s and computer clusters. The fibers will likely be “dark” for a while, but later you’ll be so glad that fiber is available.

@Bonbon99 

I have  Home Theatre setups here as follows…

• Arc, Sub, Surrounds in main Living Room
• Beam, Sub, Surrounds in Dining Room
• Beam, Sub-Mini, Surrounds in Main Bedroom
• Ray, Sub-Mini,  Surrounds in Kitchen/Diner

I have personally chosen to not wire anything and all have been working fine, I run all main players on a WiFi (802.11AX/AC mixed) mesh signal and they’ve ALL been great… if I were to decide to cable things, I would only ever wire the 4 main players in my System back to the main router (not to a satellite WiFi hub).
I would never cable any HT surrounds, or Subs, personally speaking, as I prefer to let those use the 5Ghz ad-hoc wireless connection to the bonded main player. As it stands, I’m fine with all running on wireless and (apart from the Kitchen Ray) I do have a gigabit network point in every other room, so having the wiring is always a good idea, but you may not necessarily need to use it.

Thanks Ken and everyone for the super helpful replies. What an awesome community