On average across the year, no, Vietnam is not hotter than Myanmar . Vietnam has an average temperature of 26°C/79°F and Myanmar has an average temperature of 27°C/81°F.
Vietnam's hottest month is June, with an average maximum temperature of 34°C/93°F, which is not hotter than Myanmar's hottest month (May, with an average maximum temperature of 36°C/97°F).
On average across the year, yes, Vietnam is colder than Myanmar . Vietnam has an average minimum temperature of 22°C/72°F and Myanmar has an average minimum temperature of 21°C/70°F.
Vietnam's coldest month is January, with an average minimum temperature of 17°C/63°F, which is not colder than Myanmar's coldest month (also January, with an average minimum temperature of 15°C/59°F).
On average across the year, yes, Vietnam has more rain than Myanmar. Vietnam has an average annual rainfall of 825mm and Myanmar has an average annual rainfall of 657mm.
Vietnam's wettest month is October, with an average monthly rainfall of 134mm, which is drier than Myanmar's wettest month (July, with an average monthly rainfall of 139mm).