Western Red Cedar dying - clay soil?

Looking for some help and suggesions...

I planted a row of 20 Western Red Cedar hedge plants in spring 2017 and they initially took really well but a few months in and they started to brown from the bottom up.

From doing some reading around, I suspect that the heavy clay soil is causing the roots to sit in water, effectively drowning the plants.

The place i got them from has offered to replace them so my priority now is to ensure that i can improve the ground conditions to prevent this from happening again.

So a few questions:

1) Has anyone come across this before?

2) Are there any alternatives to western Red Cedar that give year round screening and fast growing to gain some height

3) If i stick with western red cedar, what are your suggestions on improving the ground conditions to address the heavy clay soil water logging? Should i create a raised bed and build up with say a foot or two of top soil so that the roots are in better draining soil?

I’ll get some photos added up if i can work out how to.

Thanks in advance.