Abraham, 22, who has won two caps for the Three Lions in friendlies against Brazil and Germany in 2017, had flirted with switching his worldwide allegiance to the country who he qualifies for through his father.
Tomori, who previously played for Canada at Under-20 level, has impressed since being promoted to the first team by Chelsea manager Frank Lampard, having played under him on loan at Derby County last season.
Lingard was, along with Tottenham's Dele Alli and Manchester City star Kyle Walker, one of the high profile omissions from the Three Lions squad to take on Bulgaria and Czech Republic in UEFA Euro 2020 qualifiers later this month.
"There have been some hard decisions to make", Southgate said in a statement.
Tomori's invitation is the first for him to the English senior national team.
But Guardiola - who will be without midfielder Kevin De Bruyne for Sunday's visit of Wolves because of a groin injury - has admitted Walker also faces a threat to his place in City's side from summer signing Joao Cancelo. "He's played very well for Chelsea against some very good opponents".
Sterling has made a fine start to the season, scoring nine goals in 10 matches for City, including six in six in the Premier League.
"It was a bit early for him before", Southgate said. He is physically strong, fast and we have tried to help him to be a better player.
Abraham represented England at the recent European Under-21 Championships.