How to say tradeoff in Cantonese and Mandarin?
Trade-off https://www.merriam-webster.com/dictionary/trade-off
  
  1 : a balancing of factors all of which are not attainable at the same time
  
  2 : a giving up of one thing in return for another : exchange


Trade-off as a noun is 代價 in both  Cantonese and Mandarin ('trade-off' basically means "in exchange" )

Example: 

"Thicken the armor would provide better protection, but the trade-off is your speed would slow down."

"加厚护甲会提供更好的保护，但代價是你的速度会减慢。"

You can use "作為交換" (in exchange) instead of "代價是" e.g. "加厚护甲会提供更好的保护，但作為交換, 你的速度会减慢。"