I suggest that the game be cancelled.句中从句部分的be动词为什么用原形表示?用is可以吗?

不行
suggest "建议” 引导的从句中,谓语为“should +动词原形” ,should 可以省略.本句为此语法考查的最难度之一.你在not 前加should 即可.
在表示建议、命令、要求、忠告等动词的后面,其宾语从句的谓语用“should+动词原形”表示虚拟语气
　　常用的此类动词有：
　　表示“要求”的：ask,desire,request,demand,require,beg
　　表示“提议、劝告、建议”的：move,propose,suggest,recommend,advise,vote
　　表示“决定、命令”的：decide,order
　　表示“主张”的：maintain,urge
　　表示“同意、坚持”的：consent,insist
　　例：The doctor suggested that he (should) try to lose his weight.
　　He insisted that we (should ) tell him the news.
　　上述动词的名词形式,demand,desire,requirement,advice,order,decision,recommendation,suggestion,以及necessity,preference,plan,motion,idea等名词,其后的表语从句或同位语从句,也用“should+动词原形“表示虚拟语气.现代英语,特别是美国英语,常省去“should”,例：
　　The advice is that we (should) leave at once.
　　He idea that we (should)visit Great Wall was warmly welcomed.