I am becoming vegan and i'd like to know if vegan omegas (flaxseed) and vitamin d2 are good replacements for fish oil and d3.

Flax for some, NO D2. Flax & hemp seed oil are good replacements for many but not all- we need to convert the ala to epa & dha & not everyone does that well. Vegan dha from algae is available. I strongly advise against d2- see http://articles.Mercola.Com/sites/articles/archive/2011/11/30/taking-the-right-type-of-vitamin-d.Aspx vegan d3 is available.Search "plant based vitamin d3."i advise 5000 iu/day in fall & winter.