Yes, here in Canada we have an approval system for construction products that meet or exceed standards. this process is long and expensive. Demilec soya (not high lift) has received its CCMC # as a radon barrier. we have bought a spray-foam rig to service the new construction market for radon control.
Like all products in the radon world effectiveness is in the details and the competence of individual installer.
Most good sprayers are not of the small job temperament and they love to spray large quantities quickly.
so you will want to talk to several contractors. Spray-foam has some nasty chemicals while it is off gassing and owners and pets need to be out of house while it is being sprayed and for 24 hrs after completion.
I have been around construction in Canada a long time and have not seen a structural sandstone block wall could you share some pictures.
if this is what i am imagining, you may do well to provide something for the foam to hang on to as moisture and freeze/ thaw / movement of blocks may break bond of foam to blocks over time. I would ensure that the the spray foam does the rim joist cavities and spray foam in Canada must be covered with either drywall or another fire rated barrier.

To add to Bob's comments spray foam is fantastic for air/gas sealing. Here are 2 links and documents for reference. The first link is the CUFCA and NRC approval of spray foam as a Radon barrier. The second link is the detail for spray foaming a rubble foundation wall which includes a drainage plane between the foundation and the wall (which Bob suggested you have for other valid reasons). You will need to confirm local fire code requirements for what the foam needs as a fire barrier. Building Science Press and Joe Lstiburek are renowned for their competence in building science. I can't imagine a building official being able to argue with his designs.

Bob already mentioned it but I also need to repeat it. Make sure occupants are out of the building during the application of the spray foam. The isocyanates in the foam are a chemical sensitizer and you simply must control exposure during application.

https://www.demilec.ca/documents/Heatlok-Soya-HFO/CCMC-14073-R_EN_RADON-RCS.PDF

https://www.buildingscience.com/documents/insights/bsi-041-rubble-foundations

Thanks to both of you! I originally thought about it because of an article I saw regarding the Demilek Soya product. I'm going to share these two articles with my client and his foam installer. I'll post a couple of photos of the walls Wednesday night.
Thanks Bob and Bruce.

At least here, in a crawlspace, a 3" gap must be left between the foam and the floor joists for termite inspection, just the same as with rigid foam and polyethylene vapor barriers.

Thanks Henri. A great point. We need 6" in many counties here in Ohio. Most of that area is almost always above grade anyway so there is less radon entry at the top of the wall. Good advise. Oh course they don't have quite the termite problem in Canada that we do in most of the States. Thanks.