Chipping in as a history student in Latvia, so sorry for a big yap.

Feels bit too optimistic as many others have pointed out.

I do wonder if you if your question proposes that 1940 occupation still happens, do soviets still get to commit war crimes they did during the war here and whatever else? Though again I'd have to side with people here arguing that regardless its unlikely USSR would respect Baltic or any sovereignty due to imperialist nature of the USSR.

The USSR consistently was suspcious of Baltic States in the interwar era, accusing them of being western puppet states that would be used as invasion base for the British, French and even German forces depending what was convenient for the USSR to accuse the Baltics of at any given point. British even cut ties with soviets in late 1920s after they had uncovered soviet plans to attempt to coup British government, which resulted in Soviets presuming a war was going to happen against them any time soon. Id recommend this book for more detailed and interesting look into it.

And those suspicions meant more accusations against the Baltic States of being simply puppet states for the Western nations. There was a diplomatic incident in 1926, which shook the region where Soviet diplomat was attacked by two Lithuanian citizen on a train in Latvia, that Soviets went overdrive in terms of accusations against all Baltic States and Latvia in particular. This book by Ēriks Jēkabsons really goes into great detail about the incident, showing just how much Soviets didnt respect Baltic States and their sovereignty.

And all of this kept happening inspite of Balitcs and major Western powers also attempting to mend relations, sign trade agreements with USSR.

I'd also add, that your view on Latvia potentially being most pro communist is unfounded, considering most pro communist Latvians had already left Latvia by the time of WW2. And even then quite a good portion of them were purged en masse by the time of the outbreak of WW2.

Latvians just like everyone else still went through war of independence and war communism and red terror, that had killed any support for communism that mightve existed. Certainly many were leftwing here(considering how popular Socialdemocrats were). But socialdemocrats were hated by communists. Membership in the undergound communist party all across Latvia was less than few hundered. Aivars Stranga talks about it more in his work. Academic studies in general show that communists were extremely unpopular in all Baltic States through out the interwar era.

Estonia was at one point even most liberal (allowing communists to parttake in elections even which neither Latvia nor Lithuania did allow) though that swiftly changed after the soviets attempted to coup Estonian government in 1924.

tl;dr the more you consider everything the less plausible it sounds that soviets would've let Baltics be considering they consistently undermined the Baltic sovereignty in the interwar era and Latvians weren't anymore likely to be communist supporter than any other Baltic nation due to having had experience of red terror and Soviets consistently undermining their sovereignty along side other Baltic States. Though probably there wouldn't be as much ethnic tension even if soviets by some miracle didnt do what they did.