Yes, the hub is identical
Same 5x114.3 PCD and same 67.1 mm centre bore: wheels from Mazda CX-3 bolt on and centre on Mazda 3 without rings. You still need to check the offset and tyres, detailed below.
≈: width estimated from the original tyre size.
Wheel by wheel: offset and tyres
Each original wheel from Mazda CX-3 is compared with the one from Mazda 3 of the same diameter: how much closer the wheel gets to the shock absorber or how far it sticks out of the wheel arch, and whether the tyre keeps the same overall diameter.
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6.5Jx16 ET50 · 215/60R16 — Fits like the original
Compared with the original ≈6.5Jx16 ET50 on Mazda 3: shock absorber side 0 mm, wheel arch side 0 mm, tyre diameter +5.1 % : fit it with the original tyre size of Mazda 3 (205/55R16), not that of Mazda CX-3.
Comparison for guidance only (estimated width). Check in detail
Before fitting the wheels
An identical hub is not enough: offset, width and diameter change the position of the wheel, and larger calipers can touch a smaller wheel. Original wheels often use bolts or nuts with a specific seat: keep the fixings intended for the wheel, with the thread of Mazda 3 (Ecrous - 12x1.50), tightened to the torque shown on its vehicle page. Finally, check that the size is among the approved fitments for your vehicle. This comparison is for guidance only: have the fitting approved by a professional.
And the other way round: wheels from Mazda 3 on Mazda CX-3?