I am building a Pergola using all nothern white cedar. My corner posts are 6x6. I have let all my wood slowly dry inside my garage. I have cracking from drying especially in the 6x6 posts. I was told that this might occur. I intend to stain with a solid white color. I wanted to seal up those cracks to keep water and ice from causing damage and for cosmetic reasons. Last evening I purchased some MINWAX interior/exterior wood filler that comes with a hardner. Before I use this product was it a good option to fill the cracks?

All edges of will be primed and stained before final assembly and I am covering the post tops with caps to keep water off the ends.

Thanks for any advice.