That doesn’t make sense to me, since we do know that both rabbits and eggs are fertility symbols,
They may be symbols of a number of things.
I don't go into Sainsbury's, see eggs and think "fertility", but we're all different.
and it seems like a stretch to say they represented new life given by Christ.
I didn't say that bunnies do; they may well represent fertility. Though for children, they will just be seen as signs of spring - like the cute little lambs too.
Eggs and lambs can certainly both be used to illustrate the Easter story and message of new life. Eggs don't look like much on the outside but do have new life growing withing them - under the right conditions, of course. While the link with lambs and Jesus as the Lamb of God, is obvious. It's not a matter of trying to make something "pagan" represent the resurrection; it's about using what is already there - lambs and eggs - to proclaim and illustrate the Good News.
Jesus did this all the time - used illustrations from life that people would know and understand to bring a new message.
The symbols existed before Christ lived.
Eggs and lambs existed before Christ, and no doubt bunnies did too - so what?
An egg can be used to illustrate new life; fact.
It can also be used to illustrate, or represent, fertility, if that is the particular message you want to give. Maybe some people always think "fertility" when they see an egg - I usually think breakfast, but maybe that's just me.
Maybe some people think "spring" and "new life" when they see lambs, or maybe they think something different.
With the exception of bunnies, the others are SYMBOLS and can be used, or not, to illustrate, tell or link into the Easter story.