Word2Vec is an algorithm that generates vectors for words, that tend to be similar for similar words. It does not do sentences on its own.
You have more or less the following options:
- Create a sentence vector
- Compare similarity of word vectors within two sentences
Create a sentence vector
You could build sentence, paragraph or document vectors. There are different approaches to that. You could for example combine the word2vec of of the individual words. If you just want a solution you could go for gensim's doc2vec: https://radimrehurek.com/gensim/models/doc2vec.html
Other than that there are methods like concatenating all the word vectors (of a fixed length).
Similar questions:
How to calculate the sentence similarity using word2vec model of gensim with python
Compare similarity of word vectors within two sentences
One such approach is Movers Distance: Pairwise Earth Mover Distance across all documents (word2vec representations)
This seems like a good, but expensive approach.
Update: You've updated your question since to mention that you are using "SIF Embeddings" (instead of word2vec): https://openreview.net/forum?id=SyK00v5xx