A few people have confirmed that Canon will announce a new EF 70-300 f/4-5.6 IS lens this summer, most likely before the end of August.
We haven't confirmed whether or not the lens would be STM to match the EF 24-105 f/3.5-5.6 IS or USM. We hope to find out which it'll be in the coming days.
We have no information on pricing at the moment.