With so little info here it’s hard to know where to start. 
I suggest you look at the Sonos web site to get a better idea of their product range, supported voice services, stereo capabilities, weatherproofing standards etc. That’ll give you a much better idea of the products. It’ll also show you prices, and you need that as you’ve not mentioned your budget. It’ll confirm, for example, that smart speakers can be stereo-paired, and how you can set up voice control on those speakers. If you then have more specific questions, that’s the time to ask them. 

I have asked the Sonos txt contact and they say there is no solution. But when I was at my local Sonos store he said he had heard a 3rd party solution was available using a Sonos speaker

Not sure how this is such little info

What other info would help ,?

I want an outdoor smart speaker that will work with Google assistant 

The newer portable Sonos speakers like Move2 only offer Sonos Voice Control or Alexa but are IP56 rated. Google Assistant is available on older Sonos speakers. Or you might be able to use something linked to your Sonos system like a Nest Mini but I don’t know about their weatherproof standards.