A Russia in 1914 borders and different history could reach 1B. It was pushing 200M pre-WWI.
India without breakup would be looking at 2B by now.
An unpartitioned India, Yes. But I think that a Russia in 1914 borders would have peaked at 500-600 million. Maybe 700 million if it also eventually conquers and annexes Inner Manchuria. But even then, it would lose a bit of people if it eventually ended up losing Poland. But Yeah, going over 700 million is probably unrealistic without extremely massive immigration into Russia, and even then, you might only be able to get up to 750-800 million at the very most by the early 21st century, I think.
But of course you could also wait for Russia's breeders to become a larger share of Russia's total population later on.