Complex sentence: In 1843, during a depression in the British building industry, he emigrated to Canada with his wife and 10 children to what is now Toronto, Ontario, where his career flourished.
Split into simpler sentences: In 1843, during a depression in the British building industry, he came to Canada. He emigrated with his wife and 10 children to what is now Toronto, Ontario, Canada in 1843, where his career flourished.