The case is likely to be for false testimony to Congress, ie perjury. That can be a very tough case for a prosecutor to prove unless there is contemporaneous evidence that the statement was false and the perjurer knew it. That actually does happen sometimes, and actually most of the time when a perjury case is actually prosecuted, so there's little chance of the perjurer successfully claiming s/he forgot or was mistaken.
Unfortunately for Comey (but also probably fuck him, at least a little bit), that kind of case is pretty hard to negate ahead of trial. So, it's unlikely he'd be convicted, but also unlikely he'll avoid a trial. Rap/ride all that.
There will be motions to dismiss, just like Trump in his cases, but they'll be far more valid, but not necessarily grantable. There will be one based on selective prosecution that will be a lot more credible than Trump's, but those are exceedingly hard to win.