Your Hawking Radiation isn't going to be a problem. It's the theoretical radiation from the evaporation of the black hole due to virtual particle pairs spawned at the event horizon. The accretion disc is a more substantial problem, as that's where the lethal radiation would be coming from.
BUT you're assuming there's no accretion disc. Which means that the radiation wouldn't be lethal. And as other answers have noted, the event horizon for a black hole of 3 solar masses is relatively tiny - less than 10 kilometers. Unless this hits us dead on (very unlikely) then we'll be safe from getting "sucked in."
So what's the problem?
You're introducing a large, heavy object very suddenly into the orbits of all bodies in the solar system. Orbital mechanics are a delicate balance (as anyone playing Kerbal Space Program could tell you), and the pull of such a large object over time would shift everything in the solar system.
Since gravity falls off by the square of the distance, the pull of this 3 solar mass hypervelocity black hole would outweigh the pull of the sun at ~1.7 AU.
For reference, at 1.5 million miles per hour, the black hole would cross that distance in ~106 hours. Considering that the Hill Sphere of our sun is 1-2 light years out, this black hole would affect us even before it officially enters the solar system.
At best, it crosses our orbital disc perpendicular to the plane of rotation, causing minimal disruption. Depending on where it intersects and the positions of the other planets (the disc is ~3.75 lightyears across, which would take our BH 837 years to cross), there would be perturbations of orbits in some of the outer planets, the Oort cloud thrown into disarray, etc. We might see more comets and the like being sent into the inner solar system.
At worst, we get slingshotted around a black hole and it kicks the planet entirely out of its current orbit, sending us tumbling through space on a long, cold voyage.
Can we do anything about it?
Probably not. Any solutions to "save the planet" barring an "interstellar" type generational ship (currently not possible) would probably knock us out of orbit anyhow. If we can predict when, where, and at what angle it will intersect our system, we can roughly gauge just how bad it will be for us. If it hits the outskirts of the system (very likely - it's the largest target) than we'll be fine. if it's going straight through the center (bullseye!) than the we'll probably be pulled off orbit to spiral into the sun over a few million years.
A few million years?
Yeah, we'll have 1000+ years of the blackhole affecting our orbit, and with the perturbations it will take quite some time for us to be sucked in, but LONG before that the earth will have been scoured clean of life due to massive environmental destruction. I'd give it a few millenia or so. Plenty of time for humans to work on tech to move us to a different solar system.