Im not sure about an economics through arts, but an economics major through a b.comm gets very mathematical in 2nd and 3rd year. You deal with quite a lot of regressional analysis/statistics (econometrics modelling) and calculus work (ie IS/LM curve, salow swan models etc).
I would hazard a guess that an economics major through arts would deal more with the qualitative side of economics (ie. the socio-economic impact of policy changes etc.). This is purely based on the fact that a b.arts does not req methods and as such, would most likely not be too quantitative; so i could be totally wrong in this aspect.
Best way to find out is to look at the subjects (and subject codes) requires for a major in economics in each course and see if they match up. If they do, then there will be no difference in the subjects taken.