90x90 is OK for bearers and 90x45 for joists is probably OK too but you don't say what the joist span is.
However, I would either go up to 140x75 bearers and 140x45 joists or add some extra posts because of the bounce you'll probably get. I reckon it's better to over-engineer decks because you're likely to have a lot of people standing on it at BBQs etc. If you added another post and keep your joist span down, you will get away with the smaller sections.
There are span tables that give the minimum sizes for things. Of course it depends on the type of timber you are using. If you give me your joist span, I'll look it up in my copy of the span tables.
"I don't practice what I preach because I'm not the kind of person I'm preaching to."