Handling
The Volvo XC70 and the BMW have about similar tires.
With its tighter turning radius, the 3 Series is doubtless nimbler than the Volvo, something to consider if you do a lot of city driving; however, note that a vehicle with a tight turning circle may feel a bit twitchy on the highway.
Drivetrain
The Volvo's engine is markedly smaller than the BMW 3 Series's. Note that smaller engines can be stressed more; on the other hand, smaller engines are often cheaper to fix.
The BMW 3 Series could learn a lesson or two from the Volvo XC70 as far as torque.
Utility
The Volvo XC70 is a better choice than the BMW in terms of hauling capacity, especially if you frequently need to carry a lot of cargo or big dogs.
The Volvo XC70 will doubtless prove friendlier than the BMW for those of you with frequent child-cargo.
Comfort
While the front cabin in the Volvo XC70 offers a bit more head room than the BMW 3 Series, there really isn't much of a difference.
The Volvo XC70 is not particularly more spacious for your passengers than the BMW 3 Series.
Dimensions
The 3 Series is a little more ponderous than the Volvo XC70.
The BMW 3 Series's tank is approximately the same size as the Volvo's, though the Volvo's is a bit more capacious.
The BMW 3 Series and the Volvo XC70 compete for the same parking spaces.
Cost
The Volvo isn't much more expensive than the BMW 3 Series with respect to MSRP.
Overview
The Volvo XC70 and the BMW 3 Series have the same basic after-sale protection.