Can Availability Groups provide seamless failover (with no query failures)?
No, there's no way to do zero-downtime failover with AlwaysOn (or in SQL Server in general, as far as I'm aware). To do that, the SQL Server you're connected to would have to do state transfer to another node mid-query, and since many failovers are unexpected, that's not possible.

However, you can enable "read-only secondaries" in AlwaysOn, and then your readers would have zero-downtime when the primary server fails over - since they're connecting to a secondary copy anyways to do their SELECT queries, they wouldn't even notice the failover. There would still be an interruption for users with a "Write" connection open, but at least some part of your user base would be uninterrupted.