The Allied intervention force that I had planned for this operation would consist of three divisions, 1 British (actually consisting of 4 Brigades with all of their support equipment),1 French (alpine rgt, FFL Rgt, tank Bn, artillery rgts, AA BN), Polish Infantry Division ( the Polish infantry/mtn division would be made up of troops that had made their way to France and were rearmed,trained and equipped by the French) In our time line these troops were used to intervene in Norway but I have them leaving much earlier so as to have a major impact on the War in Finland.
The British government was able to supply Finland with some arms and aircraft But it is known that if the British had asked the US Govt was willing to supply 100,000 refurbished WW1 rifles used by the AEF in that war as well as 100x 75mm artillery pieces that were in excellant condition and much more modern than most of the Finnish artillery.
The allied divisions would have all of the artillery that would normally be in those divisions thus they would have a very powerful punch. In addition I would have the Royal Navy together with the French Navy provide a naval escort. Two aircraft carriers could provide an effect strike force on the soviet.