What is the best cedar to plant in Ontario to achieve a thick hedge?
Combination sun & shade
Along a fence line
Sand soil in Burlington
Can be dry conditions in the summer
Many experts recommend the native White Cedar, Thuja Occidentalis, as the most reliable of cedar hedging plants for this part of the country. It is hardy and reliable. The Toronto Master Gardeners receive many queries about cedar hedging (many focused on the Emerald Cedar) so you may find it interesting to search “Toronto Master Gardeners cedar hedges” to read others’ queries and our responses. Here is a link to an example: https://www.torontomastergardeners.ca/askagardener/hedging-for-toronto/
Because there is so much interest, the Toronto Master Gardeners have produced a gardening guide on evergreen hedges that you may also find useful: https://www.torontomastergardeners.ca/gardeningguides/evergreens-suitable-for-hedging-a-toronto-master-gardeners-guide/