  Calculations of synthetic spectropolarimetry are one means to test
multi-dimensional explosion models for Type Ia supernovae. In a recent paper,
we demonstrated that the violent merger of a 1.1 and 0.9 M$_{\odot}$ white
dwarf binary system is too asymmetric to explain the low polarization levels
commonly observed in normal Type Ia supernovae. Here, we present polarization
simulations for two alternative scenarios: the sub-Chandrasekhar mass
double-detonation and the Chandrasekhar mass delayed-detonation model.
Specifically, we study a two-dimensional double-detonation model and a
three-dimensional delayed-detonation model, and calculate polarization spectra
for multiple observer orientations in both cases. We find modest polarization
levels ($<$ 1 per cent) for both explosion models. Polarization in the
continuum peaks at $\sim$ 0.1$-$0.3 per cent and decreases after maximum light,
in excellent agreement with spectropolarimetric data of normal Type Ia
supernovae. Higher degrees of polarization are found across individual spectral
lines. In particular, the synthetic Si ii {\lambda}6355 profiles are polarized
at levels that match remarkably well the values observed in normal Type Ia
supernovae, while the low degrees of polarization predicted across the O i
{\lambda}7774 region are consistent with the non-detection of this feature in
current data. We conclude that our models can reproduce many of the
characteristics of both flux and polarization spectra for well-studied Type Ia
supernovae, such as SN 2001el and SN 2012fr. However, the two models considered
here cannot account for the unusually high level of polarization observed in
extreme cases such as SN 2004dt.
